Development of an Environmental Life-Cycle Assessment (LCA) Protocol for Flexible Pavements that Integrates Life-Cycle Components to a Proprietary Software

Significant progress has been made in research on environmental life-cycle assessment (LCA) of pavements. Use of this new knowledge has been slowed by a lack of standardized datasets and analysis protocols. Several software packages have been developed to address this by providing datasets with broader coverage and better quality, but practitioners need applicationspecific data input interfaces for easy use. The authors report work on developing a protocol for environmental LCA of flexible pavements that uses a proprietary software system with data input interface plug-ins they developed for each of the five flexible pavement life-cycle phases. This protocol allows designers to integrate environmental LCA with life-cycle cost analysis (LCCA) to select the optimum design from several alternatives. With looming transformative changes in pavement materials and technology landscapes, this protocol also has the potential to allow a more effectively holistic assessment of such novel systems. (ISO14001, 2004). The life-cycle of a product comprises of consecutive and interlinked phases from raw material acquisition or generation to product end-of-life and disposal. LCA for a product is the compilation and evaluation of inputs, outputs and their potential environmental impacts throughout its life-cycle. This systematic approach will ensure accurate assignment of a potential environmental burden to the appropriate life-cycle phase or individual process (ISO14040, 2006). The ISO 14040 LCA has the following four phases: goal and scope definition, inventory analysis, impact assessment, and interpretation. According to ISO 14040, the system boundary for an LCA must be framed to highlight key phases of the product life-cycle. This typically includes unit process for raw materials, inputs and outputs of the primary production/manufacturing/processing sequence, distribution, product use and maintenance, disposal of process wastes and used products, recovery of used products (including reuse, recycling and energy recovery), production and use of fuels, electricity and heat, manufacture of ancillary materials, manufacture, maintenance and decommissioning of capital equipment, lighting and heating (ISO14040:2006). 1.2.2 Flexible pavement life-cycle In general, a pavement life-cycle consists of six phases, all of which have significant impacts on the environment: material production, pavement design, construction, service period, maintenance/rehabilitation, and end-of-life (Harvey et al., 2016). It can be considered as a closed loop for a particular project depending on the system boundaries for which the LCA is to be conducted. Design is not identified as a separate phase in most instances, and its impact is considered to be included among the other five phases. 1.2.3 Pavement LCA Pavement LCA is an area of active interest among both researchers and practitioners, and both groups generally follow the ISO 14040 guidelines (AzariJafari et al., 2016). However, efforts of these groups are constrained by the lack of reliable data with appropriate levels of accuracy. Most sustainability studies focus on quantifying the environmental impacts and only a few address other important aspects such as design, material selection, constructability, maintenance and development of policies that promote achieving sustainability goals (Santero et al., 2011a). This situation can be addressed by standardizing the way functional units and system boundaries are established, thus paving the way for unification of LCA protocols around the world. LCA is still at its infancy in areas such as pavements, and many gaps in data and methodologies that still exist need to be addressed in order to accurately quantify their environmental impacts (Santero et al., 2011b). These gaps include misinterpretation of data due to lack of standardization and differences in analysis methods. If a common set of guidelines for data collection and analysis are agreed upon, these gaps can be further reduced and the data made more valuable to the pavement engineering community. 1.2.4 Pavement LCA with Commercial Databases A number of pavement sustainability LCA studies have used commercial software platforms primarily to get access to accurate data. However, literature suggest that the user should recognize the strengths and limitations before using them. One such limitation for US users is that many of the leading LCA software have been developed in Europe and their data and methodologies cater to conditions there (Kang et al., 2014). In other instances, some software and databases have been reported to have double counting of sustainability impacts among unit process components (Vidal et al., 2013). Furthermore, the proprietary nature of commercial LCA software makes it very difficult to automate sustainability evaluations for clients’ unique requirements (Gopalakrishnan et al., 2014). 1.2.5 Introduction of paper A review of technical literature suggests a strong need for standardized protocols to conduct LCA of pavements. The purpose of this paper is to present a software-based framework for flexible pavements in which all five phases of a pavement life-cycle (excluding the design phase) are incorporated. These phases are materials processing, construction, pavement in service, maintenance/rehabilitation, and end-of-life. Unit process flow charts were developed for each life-cycle phase and a software plug-in was developed to seamlessly integrate customer design data with the proprietary LCA software and the database to allow the calculation of sustainability metrics. This method will allow the user to easily identify key process components in each phase that show high sustainability impacts and focus on ways to minimize those impacts to make the product (i.e. the pavement) more sustainable. The software-based plug-in interfaces for the five life-cycle phases have been developed in such a way that the pavement designer can evaluate each alternative using both the LCCA and environmental LCA at the time of design, so both criteria can be used to select the optimum design. 2 LCA FRAMEWORK FOR FLEXIBLE PAVEMENTS The LCA approach is gaining ground as a viable concept to make pavements more sustainable (Huang et al., 2009). For this study, a process-based modeling approach was selected since it facilitates the assessment of every minute detail of the pavement life-cycle to assess sustainability impacts so remediation measures can be identified. The five phases of the pavement life-cycle considered here are material production, construction, pavement in service, maintenance/rehabilitation, and end-of-life. Performing all inventory analyses manually can be very time-consuming, so modeling for individual life-cycles phases was done using the commercial software platform GaBiTM (thinkstep, 2016). Many software platforms are available for inventory analysis, including GaBiTM, open LCA, Simapro, Umberto, and PaLATE. A free pavement LCA software tool, Athena Pavement LCA (Athena, 2016) is also currently available with limited data availability. Athena Pavement LCA includes data specific to Canada and selected US regions; data includes materials manufacturing, roadway construction, and maintenance life-cycle stages. Data does not include demolition and disposal of the pavement. This tool calculates environmental impacts in accordance with the US Environmental Protection Agency’s (EPA) methodology for the Reduction and Assessment of Chemical and other Environmental Impacts (TRACI). This paper is the result of a broader research study to develop and assess novel material systems for flexible pavements. The commercial software platform GaBiTM was found to offer capabilities convenient to developing process flow charts, and it also provides extensive datasets for United States to go with its robust European database. GaBiTM offers twenty-three vendor-developed databases for a wide array of industries, materials and continents, and a number of these databases are relevant for flexible pavements. The databases include Professional, Energy, End-of-Life, Manufacturing Processes, Renewable Raw Materials, Construction Materials, National Renewable Energy Laboratory (NREL) US Life-Cycle Inventory (LCI) Integrated, and Full US databases. The Full US Database allowed this research team to conduct LCA of flexible pavement systems by entering candidate pavement designs shortlisted from LCCA. The schematic in Figure 1 illustrates this analysis framework. The GaBiTM software can also identify process hotspots for more detailed analysis and conduct what-if analyses for situations such as materials and process replacement candidates. The LCA for this study used a number of sustainability metrics (balances) available in GaBiTM including climate change, ozone layer depletion, acidification, eutrophication, formation of photochemical oxidants, depletion of fossil and mineral resources, and hazardous/nonhazardous waste. The effects of these metrics can be assessed by using Institute of Environmental Sciences (CML) 2001 and TRACI methodologies commonly used for characterization of environmental impact assessment. In this study, the whole life-cycle of the pavement was considered, from material production to end-of-life scenarios, processes such as production of asphalt cement, asphalt concrete and base materials, fuel and electricity, construction and rehabilitation, pavement in service, and recycling. The Full US database in GaBiTM software (thinkstep, 2016) was used in this study because it has many complete US life-cycle inventory data sets. The GaBiTM software and the database allow the quantification of inputs (material, fuel, and electricity) required, and outputs (air, water, and soil emissions) released during the pavement life-cycle. Figure 2 illustrates the components of the flexible pavement life-cycle and its components, along with the system boundary used for LCA. Figure 1. Illustration of LCA method To conduct this study, we defined a functional unit (a comparative medium with all the properties of a system) and reference flows supporting the information for the establishment of functional units. Functional unit represents the system’s function and provides an equivalent level of function or service for comparison. The functional unit of the conventional pavement system for this study is listed in Table 1. It was defined for a principle arterial highway located in Lubbock County, Texas. The LCA software and the data entry plug-in allows the use of the corresponding electricity grid mix from the Southwest Power Pool (SPP) (US EIA, 2016). Table 1 Functional Unit